1. Field of the Invention
The present invention relates to flame retardants which are nitrogen compounds containing phosphorus and synthetic resins containing them, particularly flame retardants represented by the following general formula (I), which have thermal stability and excellent compatibility with synthetic resins.
It also relates to synthetic resins which have a superior flame retardant property by adding the above flame retardants. ##STR1## wherein,
R.sub.1 and R.sub.2 may be the same or different and are halogens or hydrocarbon groups containing 1 to 10 carbon atoms, or may be selected from R.sub.5 and R.sub.6 ;
R.sub.3 and R.sub.4 are hydrogen atoms or hydrocarbon groups containing 1 to 10 carbon atoms;
R.sup.5 and R.sub.6 are hydrogen atoms or functional groups which may be converted to esters;
A and B stand for organic residues of 0 to 10 carbon atoms; and
each of n.sub.1 and n.sub.2 is a number from 0 to 4.
2. Prior Art
Methods for preparing flame retardants and synthetic resins having flame-retardant properties by incorporating them, are known in various forms.
For example, in the case of polyesters, the methods of adding single molecular halogen compounds, or phosphoric esters such as a triphenyl phosphate or phosphoric acids such as a benzenephosphoric acid derivative during the process, are described in JP laid open No. So 56-103217 and No. So 57-125258, and JP publication No. So 52-17050.
Also, the case of polyurethanes etc., JP publications No. So 38-1750, No. So 45-9197, No. So 46-2269, No. So 52-17050 and No. So 56-43056, respectively, disclose processes for preparing flame-retardant synthetic resins by adding a flame retardant such as compounds containing halogen, nitrogen or phosphorus. At that time, the phosphorus content of the synthetic resin had to be more than 10%, preferably 10 to 20% by weight.
But, JP publication No. So 56-47917, U.S. Pat. No. 3,076,010, No. 4,157,436, No. 3,873,496 and No. 3,883,478 disclose methods of adding the above flame retardants in order to prepare flame-retardant synthetic resins, and in these methods the phosphorus content of the synthetic resins, may range from 1 to 20% by weight.
JP publication No. So 40-26335, U.S. Pat. No. 3,288,846, No. 3,257,479, describe methods for preparing flame retardants of nitrogen or phosphorus compounds for flame-retardant synthetic resins.
But, when the flame retardants produced by those prior methods are added to the synthetic resin, not only does the activity of the catalyst required for their process decrease, but also the melting point of the resulting synthetic resin is lowered remarkably. Additionally, crosslinking or gelation occurs due to a reactive functional group. Moreover, the thermal stability and the resistance to acids, bases and water is decreased. Consequently it is impossible to manufacture a product having excellent flame-retardant properties.
Besides the foregoing, methods of adding a flame retardant containing halogen compounds are described in JP laid open No. So 53-143800 and No. So 54-93194. However, in these methods there are many disadvantages in that excess flame retardants must be added and thus poisonous gas is generated. Therefore, the mechanical properties and the processibility of the resulting synthetic resins are not good.
JP publication No. So 56-106955 and U.S. Pat. No. 3,660,344 disclose a method of adding nitrogen compounds as flame retardants. However, in those cases the compatibility and the affinity between the flame retardant and the synthetic resin are poor and the flame retardant used may precipitate during the process.
Hence, there are many problems including a lowered thermal stability of the above flame retardant and discoloration of the synthetic resin, etc.
A synthetic resin such as a polyurethane foam has been widely used because of its unique quality. However, it has a disadvantage in that it has a very low level of heat tolerance.
Recently, the importance of the flame-retardant property in polyurethanes has been stressed, especially when the polyurethane is used in cars, trains, or airplanes.
As this occasion demands, when a large quantity of phosphorus or halogen compounds is added by the prior art, the nature of the polyurethane foam becomes poor and very sticky, and it especially decreases in strength. Therefore, its value as a product declines too. And when the flame retardant is used in the additive form, it is readily separated by friction and the flame-retardant effect is reduced.
Also, when the flame retardant is used in reactive form, not only does the thermal stability, the durability and the lasting quality of the polyurethane decrease, but also the similarity to polyurethane is not good and excess flame retardant must be added.
For those reasons, if the flame retardant according to prior methods is used for preparing flame-retardant synthetic resins, the quality of the products is naturally decreased.
Now, the copolymerization of synthetic resins and flame retardants is widely used in order to confer a permanent flame-retardant property to a synthetic resin. Although the foregoing disadvantages in mechanical properties of the products and the processibility are slightly reduced, this method cannot completely eliminate the disadvantages. Therefore, any prior methods that have been used do not give satisfactory results, and thus the method must be selected depending upon the circumstances.
A first object of the present invention is to provide flame retardants which are nitrogen compounds containing phosphorus and which are extremely compatible with common synthetic resins, and to enhance to flame-retardant property and thermal stability of a synthetic resin which contains nitrogen and phosphorus in a single molecule.
A second object is to provide the process by which such flame retardants are prepared.
A third object is to provide a synthetic resin which is flame-retardant as a result of the polymerization of the flame retardants with a polymer when the synthetic resin is prepared.